Recently, in terms of a safety operation of a pneumatic tire mounted on a vehicle, there are noticed vehicles each provided with a detection apparatus conducting a detection of a running state under abnormal service conditions such as lowering of a tire internal pressure, excess of a load or a running speed and the like so as to shorten the running lifetime of the tire, a detection of a running state predicting the occurrence of troubles such as burst and the like, and so on.
For example, the internal pressure monitoring apparatus monitors a tire internal pressure and calls attention to a driver by operating a warning or the like when the internal pressure lowers abnormally.
Also, as a technique for detecting an abnormal running condition in which the possibility of the occurrence of the trouble is high, WO 01/17806 A1 or the like discloses, for example, a technique of monitoring a tire temperature to judge the abnormality of the running condition when a rising ratio of the temperature or an absolute value of the temperature exceed a certain threshold value (WO 01/17806 or the like).
However, both of the above conventional detecting techniques judge whether the running condition including the tire internal pressure is merely abnormal or not, but do not quantitatively judge the abnormal degree (or a severity) of the running condition. To this end, the driver can know whether the running condition is abnormal or not at the judging time, but can not know the information on whether the continuous running at this running condition should quickly be stopped or whether the continuous running is enabled by the change of the running condition such as a deceleration or the like. Particularly, the driver can not know the information on a so-called residual lifetime of the tire that the remaining runnable distance is what kilometers if the continuous running is possible, or the information just before the tire trouble, that is, the information on a so-called end stage of the residual lifetime of the tire.
In especial, there are developed run-flat tires on the assumption that the tire can be continuously run over a certain distance even if the tire internal pressure (including that the tire internal pressure is zero (gauge pressure)) is abnormally lowered by the occurrence of puncture or the like to deform the tire into a run-flat state, for example, so-called core-type run-flat tires formed by inserting an internal support, so-called side-reinforced run-flat tires formed by arranging a reinforcing rubber on at least a sidewall portion at a side of an inner surface of the tire, so-called double run-flat tires formed by inserting another tire into an interior of the tire. In these tires, it is very important that the information on the residual lifetime and end stage of the run-flat tire during the continuous running at the run-flat state is quantitatively obtained in view of the safety operation.